In-line Finishing of Plastic Add-on Components and Metal Car Bodies

New polyurethane raw materials from Bayer allow the formulation of automotive OEM coatings that can be baked at temperatures below 100 degrees Celsius. These coatings can be used to finish metal car bodies and plastic add-on components in the same operation.

The in-line coating process could offer a solution to the problem of color matching the systems used on metal and plastic components for cars.

The usual practice in automobile manufacture is to coat the car bodies and add-on components in separate operations. The consequence for the component supplier is that he must match the optical properties - shade, brilliance and leveling - of the coatings he uses with those used on the car body, a procedure which is both time- consuming and costly.

The only real solution to this problem - which would also achieve considerable cost savings ' would be to use the same formulation and batch of coating and the same application technology for all components. The current practice is to apply a primer by electrostatic dip coating (EDC) to ensure adequate protection against corrosion, an intermediate coating (primer surfacer) and a finish comprising a basecoat and clearcoat on those parts of the car that are visible to the end customer.

Whereas the basecoat undergoes only intermediate drying, the primer surfacer and clearcoat must be baked attemperatures of between 140 and 160 degrees Celsius. However, most plastics soften at these temperatures which radically restricts the range of plastics suitable for automotive applications.

The only way to solve this dilemma is to use coatings that cure at low temperatures. The new polyurethane raw materials from Bayer fulfil the conditions for the formulation of such coatings in every respect. They can be used for all layers of the OEM finish ' from the primer surfacer to the topcoat and for noise-absorbing formulations and underbody sealing systems. All layers can be baked at temperatures below 100 degrees Celsius, thus allowing the use of a wide variety of plastics.